Avoid holding locks from croak when calling notifyListeners

[jglick]

Trying to fix

Found one Java-level deadlock:
=============================
"Handling GET /…/job/main/ from … : Jetty (winstone)-17 Job/index.jelly WorkflowJob/sidepanel.jelly HistoryWidget/index.jelly":
  waiting to lock monitor 0x00007f2714a7b680 (object 0x0000000672800000, a org.jenkinsci.plugins.workflow.cps.CpsFlowExecution),
    which is held by "jenkins.util.Timer [#5]"
    
    "jenkins.util.Timer [#5]":
      waiting to lock monitor 0x00007f26a0200300 (object 0x00000006728000a0, a java.lang.Object),
        which is held by "Handling GET /…/job/main/ from … : Jetty (winstone)-17 Job/index.jelly WorkflowJob/sidepanel.jelly HistoryWidget/index.jelly"
	
	Java stack information for the threads listed above:
	===================================================
	"Handling GET /…/job/main/ from … : Jetty (winstone)-17 Job/index.jelly WorkflowJob/sidepanel.jelly HistoryWidget/index.jelly":
	at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.isComplete(CpsFlowExecution.java:1323)
	- waiting to lock <0x0000000672800000> (a org.jenkinsci.plugins.workflow.cps.CpsFlowExecution)
	at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.getCurrentExecutions(CpsFlowExecution.java:1057)
	at org.jenkinsci.plugins.workflow.flow.FlowExecutionList$ResumeStepExecutionListener.onResumed(FlowExecutionList.java:309)
	at org.jenkinsci.plugins.workflow.flow.FlowExecutionListener.fireResumed(FlowExecutionListener.java:85)
	at org.jenkinsci.plugins.workflow.job.WorkflowRun.onLoad(WorkflowRun.java:589)
	- locked <0x00000006728000a0> (a java.lang.Object)
	at hudson.model.RunMap.retrieve(RunMap.java:273)
	at hudson.model.RunMap.retrieve(RunMap.java:65)
	at jenkins.model.lazy.AbstractLazyLoadRunMap.load(AbstractLazyLoadRunMap.java:703)
	at jenkins.model.lazy.AbstractLazyLoadRunMap.load(AbstractLazyLoadRunMap.java:685)
	at jenkins.model.lazy.AbstractLazyLoadRunMap.getByNumber(AbstractLazyLoadRunMap.java:579)
	- locked <0x00000005e55ca3f0> (a hudson.model.RunMap)
	at jenkins.model.lazy.AbstractLazyLoadRunMap.search(AbstractLazyLoadRunMap.java:537)
	at jenkins.model.lazy.AbstractLazyLoadRunMap.newestBuild(AbstractLazyLoadRunMap.java:470)
	at jenkins.model.lazy.LazyBuildMixIn.getLastBuild(LazyBuildMixIn.java:254)
	at org.jenkinsci.plugins.workflow.job.WorkflowJob.getLastBuild(WorkflowJob.java:242)
	at org.jenkinsci.plugins.workflow.job.WorkflowJob.getLastBuild(WorkflowJob.java:105)
	at hudson.model.Job.getBuildHealthReports(Job.java:1215)
	at …
	"jenkins.util.Timer [#5]":
	at org.jenkinsci.plugins.workflow.job.WorkflowRun.finish(WorkflowRun.java:629)
	- waiting to lock <0x00000006728000a0> (a java.lang.Object)
	at org.jenkinsci.plugins.workflow.job.WorkflowRun$GraphL.onNewHead(WorkflowRun.java:1068)
	at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.notifyListeners(CpsFlowExecution.java:1565)
	at org.jenkinsci.plugins.workflow.cps.FlowHead.setNewHead(FlowHead.java:164)
	at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.onProgramEnd(CpsFlowExecution.java:1342)
	- locked <0x0000000672800000> (a org.jenkinsci.plugins.workflow.cps.CpsFlowExecution)
	at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.croak(CpsFlowExecution.java:919)
	at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.loadProgramFailed(CpsFlowExecution.java:902)
	at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution$2.onFailure(CpsFlowExecution.java:879)
	at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution$2.onSuccess(CpsFlowExecution.java:867)
	at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution$2.onSuccess(CpsFlowExecution.java:855)
	at …
	at org.jenkinsci.plugins.workflow.support.pickles.TryRepeatedly.access$000(TryRepeatedly.java:48)
	at org.jenkinsci.plugins.workflow.support.pickles.TryRepeatedly$1.run(TryRepeatedly.java:114)
	at …

[jglick]

Should only be true for croak → onProgramHead → setNewHead, the case observed to cause a problem.